Agree with Vep. The S&W M&P Shield makes an excellent carry weapon. I looked at the Ruger LCP, but found it too small for my hands. Keeping with 9MM makes sense to me. My wife and I have standardized on that, so we have a common caliber for our handguns.
Another thought is a small revolver in .38 Special. I have one with a short barrel and find it an easy carry weapon when not carrying the 9MM.
Hope it helps. the main thing is to have a weapon that you are comfortable shooting.